This invention relates to a sampler for the extraction of fluid samples in flowing or static state.
There is a great need to sample liquid, for example, crude oil under substantially isokinetic conditions. Many devices exists but they do not take representative samples because they do not operate in accordance with isokinetic principles. Some, for example, use complex bypass loops with motor driven circulating pumps. Some lack facilities for possible ejection of the sample and have a longer and complex flow path to the sample receptacles. Others are not bidirectional and others are extremely complex units with many component parts. Some have no facilities for changing the quantity of samples.
For sampling under non-isokinetic conditions, samplers are known which are of relatively simple construction. One such sampler employs a block of rubbery material with a cavity therein in which a liquid sample is trapped by an advancing piston and then expelled through a passage way in the piston as the piston squashes the cavity and the rubbery block flat. However, with sufficiently prolonged use, the rubbery material deteriorates and eventually fails and, in any case, is generally unsuitable for high temperature use which can for example be encountered when sampling North Sea oil. In another sampler, a closed-ended cylinder is used in place of the rubbery block but the hydraulic shock-waves produced when the piston enters the open end of the cylinder, particularly at high sampling rates, can rupture the internal seals and even cause severe internal damage.
Another known sampling device, which is not subject to the disadvantage just mentioned, operates with rotary action to trap a liquid sample in a cylindrical sample cup by rotating a cylindrical sleeve into a first position, and then causing a piston in the sample chamber to eject the trapped sample through a passageway leading from the sample chamber. This sampler, however, suffers from a number of drawbacks, viz., constructional complexity, large bearing surfaces in sliding contact leading to increased wear and risk of jamming caused by dirt, practical sealing difficulties, and limitation on the sampling rate caused by the piston displacement speed during sample expulsion being governed by the line pressure of the pipe line or similar into which the sampler is fitted.